The invention is in the field of electronic image processing and is directed to a method for changing the size of positive and negative line elements, particularly within characters, on a black-and-white or chromatic printing page to be reproduced.
Electronic image processing is essentially composed of the image input, the input processing and the image output.
In the image input, density values D for the pixels scanned in the masters are acquired by optoelectronic pixel-by-pixel and line-by-line scanning of individual image masters (continuous tone masters) and text masters (line masters) with a black-and-white scanner for producing a black-and-white printed page.
For producing a chromatic printed page, color values R, G, B which represent the color parts xe2x80x9credxe2x80x9d xe2x80x9cgreenxe2x80x9d and xe2x80x9cbluexe2x80x9d of the pixels scanned in the chromatic masters are acquired with a color scanner by optoelectronic pixel-by-pixel and line-by-line scanning of chromatic image masters and chromatic text masters. The color values R, G, B are converted into the color separation values C, M, Y, K according to the laws of subtractive color mixing, these being the color density values of the inks xe2x80x9ccyanxe2x80x9d C, xe2x80x9cmagentaxe2x80x9d M, xe2x80x9cyellowxe2x80x9d-Y and xe2x80x9cblackxe2x80x9d K employed in the later printing process.
The density values-D or color separation values Y, M, Y, K acquired in the image input are digitalized and stored as image data files and text data files for the subsequent image processing.
Given image processing in a work station, an electronic page assembly of the images and texts to form a printed page is first implemented according to a layout plan given visual monitoring on a monitor, in that the image data file and the text data file are compiled to form an overall data data file of the printed page and are stored. The texts and text data files required for the page assembly can also be generated by an operator in the work station. The image processing also comprises gradation corrections and, potentially, color corrections and color retouching.
Following the image processing, the image output occurs with a suitable image output device, for example a color recorder for registering color separations for offset printing or with an electronic engraving machine for engraving printing cylinders for rotogravure.
The texts of a printed page generally contain positive and/or negative line elements or written characters. Positive line elements exhibit a higher density value than the density value of the background, whereas negative line elements have a lower density value compared to the density value of the background.
In practice, fine line elements are occasionally lost in printing or are only inadequately reproduced. There is therefore a demand to broaden fine line elements in the image processing such that they can be reproduced with good legibility in the printing.
Traditional methods for changing the size of positive and negative line elements on a printed page have the disadvantage that only one type of line element can be changed in size at one time on a printed page, since, for example, a broadening of positive line elements leads to undesired narrowing of negative line elements.
It is therefore an object of the invention to improve a method for changing the size of positive and/or negative line elements, particularly of written characters, on a black-and-white or chromatic printed page to be reproduced such that both positive as well as negative line elements can be optimally reproduced on a printed page regardless of the respective density values of the line elements.
According to the present invention, a method is provided for changing a size of positive or negative line elements on a black-and-white printed page to be reproduced, whereby the printed page is divided into pixels and a density value representing xe2x80x9cwhitexe2x80x9d, xe2x80x9cgrayxe2x80x9d, or xe2x80x9cblackxe2x80x9d is allocated to each pixel, and wherein each line element is comprised of at least one pixel. A type of the size change of the line elements is determined, such as a broadening or narrowing. By evaluating density values, each pixel of the black-and-white printed page is investigated to see whether it is a component part of a positive or negative line element. A corresponding positive or negative identifier is determined for each pixel that is a component part of a positive or negative line element. A copy window is defined around a substitution field comprised of at least one pixel, an expanse of the copy window determining a desired size change of the line elements. The copy window is displaced with the substitution field pixel-by-pixel across the black-and-white printed page. The density values of pixels falling into the copy window are compared to a density value of the substitution field in each window position on the black-and-white printed page. Dependent on the determined size change, based on the positive/negative identifier determined for the pixel of the substitution field and based on a result of the density value comparison, a decision is made for the pixel of the substitution field in every window position on the black-and-white printed page as to whether the density value of the substitution field should be replaced by a characteristic density value of the pixels of the copy window or by a part thereof or not. The density value of the substitution field is substituted as warranted in each window position on the black-and-white printed page.